This study is a prospective, parallel, placebo-controlled, double-blind multicenter trial with random allocation to one of two treatment limbs; 5- day iloprost or 5-day placebo. The endpoints for efficacy will be: (1) reduction in total duration of Raynaud's attacks, and/or Raynaud's condition scores, (2) reduction in number of cutaneous ischemic finger lesions (ulcers, fissures, and paronychia), (3) improvement in quality of life, and (4) increased tolerance to cold.